Patent application title: CATHODE EVAPORATION MACHINE

Abstract:

The invention relates to a cathode evaporation machine, comprising an
evaporation chamber (2), a cathode element (3), an anode (4), and a
magnetic guidance system to guide the arc on the cathode element (3). The
magnetic guidance system comprises a central pole (14) and a peripheral
pole (12) with an end surface (12a). The distance (A) between said end
surface (12a) and the cathode element (3) is at least 20 mm.

Claims:

1. A cathode evaporation machine, comprising an evaporation chamber (2)
configured to house a part or surface to be coated (1), a cathode
assembly comprising a cathode element (3), and an anode (4),the cathode
assembly and the anode being configured and arranged such that an arc can
be established between the anode (4) and the cathode element (3) to cause
an at least partial evaporation of the cathode element (3),the cathode
assembly further comprising a magnetic guidance system to guide the arc
on the cathode element (3),said magnetic guidance system comprising a
magnetic device comprising a central pole (14) and a peripheral pole
(12), and at least a first magnetic field generator and a second magnetic
field generator configured to generate respective magnetic field
components contributing to a total magnetic field in correspondence with
the cathode element (3), at least said first magnetic field generator
comprising at least a first coil (13) arranged around at least one part
(14b) of the magnetic device and configured to generate the corresponding
magnetic field component in said magnetic device, such that by modifying
a current through said first coil (13), said total magnetic field in
correspondence with said cathode element (3) can be modified,the
peripheral pole (12) having an end surface (12a) configured so that the
magnetic field generated by the first magnetic field generator and second
magnetic field generator has a higher intensity in correspondence with
said end surface (12a) than in correspondence with adjacent surfaces of
the magnetic device;characterized in thatthe distance (A) between said
end surface (12a) and the cathode element (3) is at least 20 mm.

2. The cathode evaporation machine according to claim 1, wherein said
distance (A) is at least 30 mm.

3. The cathode evaporation machine according to claim 2, wherein said
distance (A) is at least 40 mm.

4. The cathode evaporation machine according to claim 3, wherein said
distance (A) is more than 40 mm and less than 150 mm.

5. The cathode evaporation machine according to claim 4, wherein said
distance (A) is more than 40 mm and less than 75 mm.

6. A cathode evaporation machine according to any of the previous claims,
wherein said end surface (12a) is spaced a distance (B) of at least 10 mm
from the outermost level of the cathode element (3), in a first direction
perpendicular to said level.

7. The cathode evaporation machine according to any of the previous
claims, wherein said end surface (12a) is spaced a distance (C) of at
least 10 mm from the cathode element (3), in a direction parallel to the
general extension of said cathode element (3).

8. The cathode evaporation machine according to any of the previous
claims, wherein the magnetic device comprises a support (15) having said
peripheral pole (12) and said central pole (14), said support having a
base (15a) from which a central protuberance (14b) forming said central
pole (14) extends.

9. The cathode evaporation machine according to claim 8, wherein the
support further has a peripheral extension (12b) extending from the base
(15a) in a direction substantially parallel to the central protuberance
(14b), said peripheral extension (12b) forming the peripheral pole (12).

10. The cathode evaporation machine according to claim 8 or 9, wherein
said at least one coil (13) surrounds said central protuberance (14b).

12. The cathode evaporation machine according to any of claims 8-11,
wherein said support (15) has a general circular configuration.

13. The cathode evaporation machine according to any of claims 8-12,
wherein the support (15) has a substantially E-shaped cross section, a
central arm of the E corresponding to the central protuberance (14b), and
the side arms (12b) of the E corresponding to the peripheral pole (12).

14. The cathode evaporation machine according to any of claims 8-13,
wherein the support (15) is made of a ferromagnetic material.

15. The cathode evaporation machine according to claim 14, wherein the
second magnetic field generator comprises at least a second coil (16)
surrounding a part of the support other than the central protuberance
(FIG. 15), the second magnetic field generator comprising said second
coil (16).

16. The cathode evaporation machine according to any of claims 8-13,
wherein the support is formed in part by ferromagnetic material and in
part by permanent magnet material, said second magnetic field generator
comprising said permanent magnet material.

23. The cathode evaporation machine according to any of claims 8-22,
wherein the protuberance has an end surface (14a) spaced from the base,
said surface being substantially planar and substantially parallel to the
cathode element (3).

24. The cathode evaporation machine according to any of claims 8-23,
wherein the protuberance (14b) has at least one through channel (17) to
allow the passage of a coolant fluid.

25. The cathode evaporation machine according to any of the previous
claims, wherein the peripheral pole (12) is located in correspondence
with a peripheral edge of the cathode element (3), but spaced from said
peripheral edge:

26. The cathode evaporation machine according to any of the previous
claims, further comprising a system of ducts (9, 10) for the passage of a
coolant fluid in correspondence with the cathode element (3).

27. The machine according to any of the previous claims, further
comprising a programmable system (18) to supply current to the first coil
(13).

28. The machine according to any of the previous claims, wherein the
peripheral pole (12) and the central pole (14) are located outside the
evaporation chamber.

Description:

TECHNICAL FIELD OF THE INVENTION

[0001]The invention is encompassed in the field of arc evaporators and,
more specifically, in the field of arc evaporators including a magnetic
guide system of the arc.

BACKGROUND OF THE INVENTION

[0002]The arc evaporators are machines intended for evaporating an
electrically conductive material, such that said material can move
through a chamber (in which a vacuum or very low pressure state is
usually established) to be deposited on a surface of a part to be coated
with the material. In other words, this type of machine is used for
coatings of parts and surfaces.

[0003]The arc evaporator machines usually comprise, in addition to the
chamber itself, at least one anode and at least one cathode between which
an electric arc is established. This arc (which in a typical case can
represent an 80 A current which is applied under a 22 V voltage) impacts
on a point of the cathode (known as the cathode point) and causes at said
point an evaporation of the material of the cathode. Therefore, the
cathode is formed from the material which is to be used for the coating,
normally in the form of a plate (for example, in the form of a disc) of
said material. To maintain the arc and/or to aid in establishing the arc,
a small amount of gas is usually introduced in the chamber. The arc
causes an evaporation of the material in the inner surface of the cathode
(i.e., on the surface of the cathode that is in contact with the inside
of the chamber), in correspondence with the points where the arc impacts
on the surface. This inner surface can be opposite the part or surface
which is to be coated, so that the material vaporized by the arc is
deposited on said part or surface. To prevent overheating of the cathode,
a coolant fluid (for example, water) is frequently applied on the
cathode, for example, on the outer surface of the cathode.

[0004]At all times, the arc (or, in the case of a system with multiple
arcs, each arc) impacts on a specific point in which the evaporation of
the cathode occurs. The arc moves on the inner surface of the cathode,
causing a wearing away of said surface in correspondence with the path
followed by the arc in its movement. If no type of control is applied on
the movement of the arc, said movement can be random, causing a rather
non-homogenous wearing away of the cathode, which can involve poor
utilization of the material of the cathode, the cost of which per unit
can be rather high.

[0005]To prevent or reduce the random nature of the movement of the arc
for the purpose of making the wearing away of the cathode more
homogenous, control or magnetic guidance systems for controlling the
movement of the arc have been developed. These guidance systems form and
modify magnetic fields affecting the movements of the electric arc,
whereby making it possible that the wearing away by evaporation of the
cathode is more homogenous. In addition, these magnetic guides contribute
to increasing the reliability of the arc evaporator, by making it
impossible or difficult for the arc to move accidentally to a point that
does not form part of the evaporation surface.

[0006]There are several patent or patent application publications that
describe different systems of this type.

[0007]U.S. Pat. No. 4,673,477 describes a magnetic guidance system using a
permanent magnet which is moved by mechanical means in the rear part of
the plate to be evaporated, such that the variable magnetic field
generated by this permanent magnet causes a guidance of the electric arc
on the cathode. This machine optionally also incorporates a magnetic
winding surrounding the plate of the cathode for the purpose of
reinforcing or reducing the force of the magnetic field in a direction
perpendicular to the active surface of the cathode and to thus improve
the guidance of the electrode. A problem of this machine is that the
magnetic system of mobile permanent magnets is very mechanically complex
and, therefore, expensive to implement and susceptible to breakdowns.

[0008]U.S. Pat. No. 4,724,058 relates to a machine with a magnetic guide
incorporating coils placed in the rear part of the cathode plate, guiding
the electric arc in a single direction parallel to that followed by the
coil. For the purpose of reducing the preferred wearing away effect in a
single path, methods which attempt to weaken the guidance effect of the
magnetic field are used such that a random component is overlaid on the
field. Specifically, it has been provided that the magnetic field
generated by the coil connects and disconnects such that most of the time
the arc moves over the cathode randomly. A problem of this machine is
that the guidance finally occurs for very little time, whereby it cannot
guarantee precise and efficient control of the wearing away of the
cathode plate.

[0009]U.S. Pat. No. 5,861,088 describes a machine with a magnetic guide
including a permanent magnet located in the center of the target and in
its outer face, and a coil surrounding the mentioned permanent magnet,
the assembly forming a magnetic field concentrator. The system is
complemented with a second coil placed in the exterior of the evaporator.
A problem of this machine is that the generated magnetic field is weak,
which involves a weak guidance effect on the movement of the electric
arc.

[0010]WO-A-02/077318 (FUNDACION TEKNIKER, et al) (corresponding to
ES-T-2228830 and EP-A-1382711) describes an evaporator with a powerful
operative magnetic guide using permanent magnets in a forward position
which corresponds to the inside of the chamber, therefore it is necessary
to incorporate means to cool the magnets when the chamber is used for
coatings carried out at a high temperature (for example, for cutting
tools, which require process temperatures of about 500° C.).

[0011]U.S. Pat. No. 5,298,136 describes a magnetic guide for thick targets
in circular evaporators, comprising two coils and a magnetic part with a
special configuration which adapts to the edges of the target to be
evaporated, such that the assembly operates with a single magnetic
element, with two magnetic poles. However, for example, it has been
verified that at least one of the alternative configurations which are
described in U.S. Pat. No. 5,298,136 is perhaps not adequate or suitable
for moving the arc in a cathode arc evaporator. Specifically,
computational analyses have been performed by finite elements of the
magnetic fields, suggesting that the configuration shown in FIG. 5 of
U.S. Pat. No. 5,298,136 in practice does not allow the movement of the
path of the arc more than just a few millimeters; therefore this
configuration involves an inefficient use of the evaporation target. The
configuration of FIG. 5 of U.S. Pat. No. 5,298,136 is formed by a
ring-shaped permanent magnet arranged such that it surrounds the target
or cathode, and the end edge of which is at the same level as the active
surface of the cathode or target. The second magnetic pole is located
inside the permanent magnet. There is arranged in contact with the lower
surface of the target and on it, and also being inside the permanent
magnet, a coil resting on a support, formed as a base of the magnetic
pole. In this configuration, the second magnetic pole a nd the co il are
placed against the target at its lower face, and the permanent magnet
clamps, with contact, the coil and the target. Furthermore, the upper
edge of the magnet is flush with the active surface of the target.

[0012]In view of the deficiencies or imperfections of the known systems,
the object of the invention is to provide an alternative configuration
which, with a rather simple structure, allows controlling the cathode arc
and moving it over a broad area of the cathode plate. More specifically,
the invention provides a system which allows guiding the cathode point
(the point of impact of the arc on the cathode) according to a path which
can be chosen individually from among an infinite number of possible
paths and which can span the entire inner surface of the cathode plate.

DESCRIPTION OF THE INVENTION

[0013]The invention relates to a cathode evaporation machine, comprising
an evaporation chamber configured to house a part or surface to be
coated, a cathode assembly comprising a cathode element, and an anode.
The cathode assembly and the anode are configured and arranged such that
an arc can be established between the anode and the cathode element to
cause an at least partial evaporation of the cathode element, and the
cathode assembly further comprises a magnetic guidance system to guide
the arc on the cathode element. This magnetic guidance system comprises a
magnetic device comprising a central pole and a peripheral pole, and at
least a first magnetic field generator and a second magnetic field
generator configured to generate respective magnetic field components
contributing to a total magnetic field in correspondence with the cathode
element. At least the first magnetic field generator comprises at least a
first coil arranged around at least one part of the magnetic device and
configured to generate the corresponding magnetic field component in the
magnetic device, such that by modifying a current through the first coil,
the total magnetic field in correspondence with the cathode element can
be modified. The peripheral pole has an end surface configured so that
the magnetic field generated by the first magnetic field generator and
second magnetic field generator has a higher intensity in correspondence
with said end surface than in correspondence with adjacent surfaces of
the magnetic device.

[0014]According to the invention, the distance between this end surface
and the cathode element is at least 20 mm. It has been verified that with
this separation between the end surface in question and the cathode
element, a considerable increase of the possibilities of moving the point
of attack of the electric arc on the cathode element is achieved; in
principle, it may be possible to move the point of attack of the electric
arc on the entire surface of the cathode element.

[0015]The distance between this end surface and the cathode element can be
at least 30 mm, or at least 40 mm. For example, this distance can be more
than 40 mm and less than 150 mm, for example, more than 40 mm and less
than 75 mm. These distances generally allow obtaining good movement of
the point of attack of the cathode arc, on the entire or substantially
the entire surface of the cathode element.

[0016]According to a possible aspect of the invention, the end surface can
be spaced at least 10 mm from the outermost level of the cathode element
in a first direction perpendicular to said level. Also or alternatively,
said end surface can be spaced at least 10 mm from the cathode element in
a direction parallel to the general extension of said cathode element.
These configurations allow obtaining a broad movement of the point of
attack of the electric arc on the surface of the cathode element.

[0017]The magnetic device can comprise a support having the peripheral
pole and the central pole, the support having a base from which a central
protuberance forming the central pole extends. The support can further
have a peripheral extension extending from the base in a direction
substantially parallel to the central protuberance, said peripheral
extension forming the peripheral pole. Said at least one coil can
surround the central protuberance. The central protuberance can comprise
a ferromagnetic material.

[0018]The support can have a general circular configuration and/or a
substantially E-shaped cross section (in which case the central arm of
the E corresponds to the central protuberance and the side arms of the E
correspond to the peripheral pole).

[0019]The support can be made of a ferromagnetic material. The second
magnetic field generator can comprise at least a second coil surrounding
a part of the support different from the central protuberance, the second
magnetic field generator comprising said second coil.

[0020]The support can be formed in part by ferromagnetic material and in
part by permanent magnet material, in which case the second magnetic
field generator can comprise the permanent magnet material. For example,
the peripheral pole can comprise permanent magnet material.

[0021]The peripheral extension can comprise, at least partially, permanent
magnet material. This permanent magnet material can have a magnetization
direction perpendicular to the base or, for example, a magnetization
direction at an acute angle with regard to the base.

[0022]In some possible embodiments of the invention, the central
protuberance can at least partially comprise permanent magnet material,
and/or the base can at least partially comprise permanent magnet
material.

[0023]The protuberance can have an end surface spaced from the base, said
surface being substantially planar and substantially parallel to the
cathode element.

[0024]The protuberance can have at least one through channel to allow the
passage of a coolant fluid (for example, water).

[0025]The peripheral pole can be located in correspondence with a
peripheral edge of the cathode element, but spaced from said peripheral
edge.

[0026]The machine can further comprise a system of ducts for the passage
of a coolant fluid in correspondence with the cathode element, and/or a
programmable system to supply current to the first coil.

[0027]The peripheral pole and the central pole can be located outside the
evaporation chamber.

DESCRIPTION OF THE DRAWINGS

[0028]To complement the description and for the purpose of aiding to
better understand the features of the invention according to practical
embodiments thereof, a set of drawings is attached as an integral part of
said description in which the following has been depicted with an
illustrative and non-limiting character:

[0029]FIG. 1 shows a schematic sectional depiction of a circular arc
evaporator with an external powerful magnetic guide according to a
possible embodiment of the invention.

[0030]FIG. 2 shows a configuration corresponding to the state of the art
(specifically, corresponding to FIG. 5 of U.S. Pat. No. 5,298,136).

[0031]FIG. 3 shows an image of a magnetic field created by a configuration
according to FIG. 1, as results by calculating it by finite elements.

[0032]FIG. 4, similarly to FIG. 3, shows an image of a magnetic field
created by the configuration shown in FIG. 2 (calculated by finite
elements; the same software package has been used to calculate the fields
shown in FIGS. 3 and 4).

[0033]FIG. 5 shows a graph of a magnetic field perpendicular to the
surface of the evaporation target, calculated in the surface of the
target, depending on the distance from the center of the target and for
different currents circulating through the coil shown in FIG. 1.

[0034]FIG. 6, similarly to the previous figure, shows a graph of the
magnetic field perpendicular to the surface of the evaporation target,
calculated in the surface of the target, depending on the distance from
the center of the target and for different currents circulating through
the inner coil of the magnetic configuration of FIG. 2.

[0035]FIG. 7, similarly to FIGS. 5 and 6, shows a graph of the magnetic
field S perpendicular to the surface of the evaporation target,
calculated in the surface of the target, depending on the distance from
the center of the target and for different currents circulating through
the outer coil of the magnetic configuration described in U.S. Pat. No.
5,298,136.

[0036]FIGS. 8-14 show several alternative configurations of the magnetic
device.

[0037]FIG. 15 shows an alternative configuration of the invention in which
permanent magnets are not used, its function is carried out by a coil
outside the ferromagnetic core.

PREFERRED EMBODIMENT OF THE INVENTION

[0038]FIG. 1 shows a machine according to a preferred embodiment of the
invention, comprising an evaporation chamber 2 configured to house a part
or surface to be coated 1, a cathode assembly comprising a cathode
element 3, and an anode 4. The cathode element and the anode are
connected to the negative and positive poles, respectively, of an
electric power source 100, suitable for establishing and maintaining,
under certain conditions, an electric arc between the cathode element 3
and the anode 4. Associated to the chamber there is a system of vacuum
pumps 101 to establish a vacuum condition (or, better said, substantially
vacuum condition) inside the chamber 2, as well as a gas injection system
102 to inject a small amount of gas, which can serve to facilitate
establishing the electric arc between the cathode element 3 or cathode,
and the anode 4 of the system.

[0039]The cathode element 3 forms what is usually referred to as the
"target" to be evaporated, at least partially, with the cathode arc. The
cathode element is located in an opening in one of the walls of the
chamber 2, placed in a ring 7 screwed in a coolant part 8, associated to
an inlet duct 9 of a coolant fluid, and to an outlet duct 10 of the
coolant fluid, which passes between said inlet and outlet in contact with
an outer surface of the cathode element to cool it. A part 5 made of
plastic or ceramic material serves to fix the cathode assembly to the
wall of the evaporation chamber 2; this part 5 provides electric
insulation between the cathode assembly and the body of the chamber 2. In
addition, the machine incorporates a protective plate 6, which can be
made of boron nitride or of another suitable material, and which is
located to protect the side of the cathode element 3 and the ring 7, such
that the electric arc cannot impact on these parts of the assembly. This
protective plate must be subject to periodic maintenance because in the
course of operation of the arc it is gradually coated with electrically
conductive materials, whereby its electric insulation and its
effectiveness to prevent the striking of the arc gradually decrease.

[0040]Logically, and even though they are not shown in the figures, placed
between the coolant part 8 and the cathode element there is at least one
sealing joint to prevent the coolant fluid from being able to pass into
the chamber 2.

[0041]In addition, the cathode assembly further comprises the magnetic
guidance system to guide the arc on the cathode element 3. Specifically,
in the embodiment shown in FIG. 1, this magnetic guidance system
comprises a magnetic device comprising a central pole 14 and a peripheral
pole 12, and a first magnetic field generator and a second magnetic field
generator configured to generate respective magnetic field components
contributing to a total magnetic field in correspondence with the cathode
element 3. The first magnetic field generator comprises a first coil 13
arranged around a central protuberance 14b extending from a base 15a of a
support 15 forming part of the magnetic device. This protuberance 14b is
configured to generate the corresponding magnetic field component in said
magnetic device, such that by modifying a current through the first coil
13, the total magnetic field in correspondence with the cathode element 3
can be modified. The central protuberance 14b has an end surface 14a
spaced from the base 15a; this surface is substantially planar and
substantially parallel to the cathode element 3. In addition, the
peripheral pole 12 has an end surface 12a configured so that the magnetic
field generated by the first magnetic field generator and second magnetic
field generator has a higher intensity in correspondence with this end
surface 12a than in correspondence with adjacent surfaces of the magnetic
device.

[0042]The support has a peripheral extension 12b extending from the base
15a in a direction substantially parallel to the central protuberance
14b; this peripheral extension 12b forms the peripheral pole 12. In this
preferred embodiment, the peripheral extension is formed by permanent
magnets and ends in the mentioned end surface 12a.

[0043]The magnetic device thus basically comprises a peripheral ring of
permanent magnets, overlaid on an electromagnet with a body with a
T-shaped cross section (forming the support 15 with its central
protuberance 14b), made of a material with high magnetic permeability and
little coercivity (for example, soft iron or another suitable
ferromagnetic material) and with the central arm of the T surrounded by
the coil 13.

[0044]Furthermore, the cathode assembly is provided with a programmable
system 18 to supply current to the first coil 13. The programmable system
can comprise an amplifier of t he type normally used for feeding DC
motors, and delivering a current controlled by a signal which is sent
from a Programmable Logic Controller (PLC), such that it is possible to
vary the current circulating through first coil 13 in a programmed
manner.

[0045]According to the invention, the permanent magnets are located in
correspondence with the outer edge of the cathode element, but spaced
from the cathode element. Specifically, the distance A between the end
surface 12a (corresponding to an end of the permanent magnets) and the
cathode element 3, is at least 20 mm, for example, between 40 mm and 150
mm. It is appropriate that the end surface 12a is spaced a distance B of
at least 10 mm from the outermost level of the cathode element 3, in a
first direction perpendicular to said level, and a distance C of at least
10 mm from the cathode element 3, in a direction parallel to the general
extension of said cathode element 3, as indicated in FIG. 1.

[0046]This configuration allows establishing a point of attack of the arc
which can be moved on the entire surface of the cathode element which is
accessible from inside the chamber 2, and it further allows placing the
cooling system 8 between the magnetic guidance system and the cathode
element 3.

[0047]As can be seen, the magnetic guidance system of FIG. 1 is completely
outside the evaporation chamber 2, which facilitates the design and
manufacture of the machine.

[0048]FIG. 1 is a schematic drawing in which its relative proportions
approximate the proportions of the evaporator for a circular evaporation
target with a diameter of 100 mm.

[0049]FIG. 2 shows by way of example an embodiment which seems to form
part of the state of the art and which, more specifically, seems to be
reflected in U.S. Pat. No. 5,298,136. This system comprises a cathode or
evaporation target 72, a ferromagnetic core 75, a coil 76 and permanent
magnets 71. The permanent magnets 71 are at the same level as the surface
of the cathode element 72, which has been considered to be unsuitable for
many applications because it does not seem to favor suitable guidance of
the arc on the entire surface of the cathode element.

[0050]FIG. 3 shows the lines of the magnetic field created by the
permanent magnets when the coil is inactive, in the magnetic
configuration according to the embodiment of the invention shown in FIG.
1. The magnetic field has been calculated with a software package for
calculating magnetic fields by finite elements. Point "P" indicates the
point in which the magnetic field is parallel to the inner surface of the
target (i.e., to the surface of the cathode element that is located in
correspondence with the inside of the chamber and on which the cathode
arc must act), or, in other words, the point of the surface of the target
in which the normal component of the magnetic field (perpendicular to the
surface of the target) is cancelled out. These points form a circular
path on the surface of the target, which forms the path that the electric
arc will follow in its movement.

[0051]FIG. 4 shows the lines of the magnetic field created by the
permanent magnets when the coil is inactive, in the magnetic
configuration shown in FIG. 2; the magnetic field has been calculated
with the same software that has been used to calculate the magnetic field
shown in FIG. 3. Also in FIG. 4, point "P" indicates the point in which
the magnetic field is parallel to the inner surface of the target.

[0052]The relative proportions of the parts appearing in FIG. 2 are not
suitable for powerful permanent magnets, such as those manufactured from
a neodymium-iron-boron or a cobalt-samarium base. It is possible that
FIG. 5 of U.S. Pat. No. 5,298,136 is drawn thinking of the use of Alnico
magnets, which were still the most frequent magnets at the time the
corresponding patent application was filed. Therefore, when the
simulations on which FIGS. 3 and 4 are based were made, Alnico V
permanent magnets have been assumed. To assure that both simulations are
comparable, a target with a diameter of 100 mm has further been used for
both. Taking this as a reference, the simulation for FIG. 2 has been
carried out conserving the proportions between the parts appearing in
FIG. 5 of U.S. Pat. No. 5,298,136.

[0053]FIG. 5 shows a graph of the normal component of the magnetic field
in the surface of the target ("y" axis, in Teslas (T)), depending on the
distance from the center of the target ("x" axis, in mm), for different
values of current density (2 A/mm2, 0 A/mm2 and -1 A/mm2,
respectively) made to circulate through the coil, all for the magnetic
configuration shown in FIG. 1. As previously indicated, the arc will
follow the path formed by the points in which the magnetic field is
parallel to the surface of the target, i.e., the points where the normal
component is cancelled out. Therefore, it can be seen in this graph that
for an inactive coil, J=0 A/mm2 the path is a circumference of 44 mm
in radius. Similarly, for J=-1 A/mm2, the path has a radius of 48
mm, very close to the edge of the target, whereas for J=2 A/mm2 the
radius of the path is 3 mm, therefore it is virtually in the center.

[0054]In contrast, FIG. 6 shows the same graph (i.e., a graph of the
normal component of the magnetic field in the surface of the target -"y"
axis, in Teslas-, depending on the distance from the center of the target
-"x" axis, in mm-, for different values of current density (J=2
A/mm2, 0 A/mm2, -2 A/mm2, -5 A/mm2, respectively)
which is made to circulate through the coil) for the magnetic
configuration of FIG. 2 (applying what has been mentioned above with
regard to that figure, mutatis mutandis). As can be seen, for all the
reasonable values of currents in the coil, the normal magnetic field is
cancelled out for a radius of about 44 mm, therefore the arc will follow
this circular path independently of the intensity of the current
circulating through the coil. The only modification that is obtained by
varying the intensity of the coil is a slight increase or reduction of
the intensity of the magnetic field, which will have a small influence on
the degree of strength with which the magnetic field secures the arc to
the established path, and it will also slightly influence the speed at
which the arc moves when varying the intensity of the parallel magnetic
field.

[0055]FIG. 7 again shows a graph of the normal magnetic field for the
magnetic configuration of FIG. 2 (namely, a graph of the normal component
of the magnetic field in the surface of the target -"y" axis, in Teslas-,
depending on the distance from the center of the target -"x" axis, in
mm-, for different values of current density (2 A/mm2, 0 A/mm2
and -2 A/mm2, -5 A/mm2 respectively) which is made to circulate
through the coil) for the magnetic configuration of FIG. 2 (applying what
has been mentioned above with regard to that figure, mutatis mutandis),
but this time using a coil outside the ferromagnetic core. In this case
there is an exiguous variation in the radius of the path of the arc, from
40 mm in radius to 45 mm, despite the fact that the intensity must be
varied to that end between -2 A/mm2 and 5 A/mm2, i.e., much
more than in the configuration of FIG. 1. This means that if one is based
on the system proposed in FIG. 2, it may possibly be necessary to adopt
cooling systems with water to prevent the coils from overheating due to
the mere passage of the current.

[0056]The main reason for the inability to vary the path of the arc with
the action of the coils in the case of the configuration of FIG. 2 may
reside in the fact that the nearness of the permanent magnet (the field
of which is barely altered by the coils) to the surface of the target
makes the magnetic field in this point barely be affected by the field
created by the coils. Therefore, the invention solves this problem by
moving said permanent magnets (or the functionally corresponding elements
of the magnetic device) away from the evaporation target. To offset the
weakening of the magnetic field associated to the moving away of the
permanent magnets, it may be appropriate to increase the size thereof. It
is estimated that in the case of FIG. 1, a separation of 20 mm between
the permanent magnets and the target can be sufficient so that the action
of a suitably designed coil can sweep the path of the arc in a range of
practical utility. Moving it farther away can give a larger sweep range,
but in return the magnetic field is reduced, therefore its beneficial
effects on the performance of the arc decrease, or alternatively, it is
necessary to incorporate larger or more powerful magnets. It is commonly
considered that a guide with a parallel magnetic field, in the path of
the arc, of about 15 Gausses (0.0015 Teslas) can be sufficient to
suitably guide the arc, but the increase of the intensity of the magnetic
field normally results in an improvement of the coating. In return, this
requires the use of larger magnets or magnets with more energy, and even
arc supply sources of better quality since the increase of the movement
speed of the arc also involves an increase in the voltage of the arc and,
therefore, in its instability, which must be offset by using a more
reactive supply source of better quality. Therefore the choice of the
magnetic intensity which must be used depends on the relative importance
given to the different factors that have been mentioned.

[0057]FIGS. 8-15 show some alternative configurations for the manufacture
of the magnetic part of the magnetic guide, out of the many that can be
conceived, essentially maintaining the character of the invention.

[0058]FIG. 8 corresponds to an alternative embodiment of the magnetic
guide in which the ferromagnetic core has a central through opening 17,
through which the supply 9 and the return 10 of the coolant fluid can
pass, as well as the supply of the current of the arc (which is not
shown). The opening barely modifies the distribution of the magnetic
field in the surface of the target and its impact in the sweep of the
surface is very low, whereas this form of supply of the coolant fluid and
of the current of the arc allows it to be carried out symmetrically,
homogeneously, not affecting the wearing away profile of the target. The
cooling can be sophisticated using radial or spiral channels. As in FIG.
1, the peripheral extension 12b is formed by permanent magnets.

[0059]FIG. 9 shows a configuration in which the Alnico magnets used in the
simulation (which form the peripheral extension in FIG. 8) have been
replaced with a ferromagnetic part (forming part of the actual support
15) capped with a high-energy magnet 12c manufactured in
neodymium-iron-boron or in cobalt-samarium, having the advantage of
providing more energy and preventing the demagnetization problems of the
Alnico magnet.

[0060]FIG. 10 shows a configuration similar to FIG. 9 but in which magnets
14c have also been added in the central pole, which contributes to
increasing the intensity of the magnetic field.

[0061]FIG. 11 is an alternative configuration to that of FIG. 10, in which
the magnets 14d of the central pole are radially magnetized, therefore a
larger number of magnets can be placed, which aids in further increasing
the field.

[0062]In these configurations the magnetization of the permanent magnets
located in the central pole is such that it coincides with the direction
in which the magnetic lines created by the peripheral magnets 12c arrive
such that they reinforce them, without substantially modifying the
distribution of lines created by the peripheral magnets 12c. If these
magnets of the central pole 14c, 14d were magnetized in the reverse
direction, they would oppose the flux created by the peripheral magnets
12c and could substantially alter the character of the magnetic field.

[0063]FIG. 12 shows a configuration in which the peripheral magnets 12d
are not magnetized vertically but rather with a certain inclination
towards the center of the evaporator. This alteration modifies the
location of the path created simply by the peripheral magnets, which can
be advantageously used to equal the intensity that the coil must apply in
both directions to drag the path to its practical limits.

[0064]FIG. 13 shows a configuration in which the permanent magnets 12e are
located in the horizontal plane instead of in the vertical arms. This
configuration has the advantage of providing a large volume for the
placement of magnets, therefore the latter can be lower energy magnets
than those used in other configurations. For example, they can be of hard
ferrites, instead of neodymium-iron-boron, which could be used in other
configurations.

[0065]FIG. 14 shows a configuration in which magnets are not used in the
peripheral pole and the central pole is formed by a permanent magnet 14e
with a magnetization that does not have to be strictly vertical but
rather can be inwardly inclined.

[0066]FIG. 15 shows a configuration in which permanent magnets have been
discarded and their function is carried out by a coil 16 outside the
magnetic assembly formed by the ferromagnetic core forming the support
15. Despite having less practical utility than the rest of the
configurations described, circumstances can arise in which the extra
flexibility provided by the outer coil can be advantageously used.

[0067]Additionally, all these configurations can be made compatible with a
gas injection system through an insert placed in the center of the
evaporation target to allow carrying out electronic ignition of the arc.

[0068]The configurations that have been described can even be combined
with one another to create valid configurations, therefore it is obvious
that the described configurations by no means deplete the possibilities
of manufacturing different magnetic guides that substantially adapt to
what has been described in this invention. Identical or similar elements
have been indicated in this detailed description of several possible
embodiments of the invention with the same reference numbers.

[0069]In this text the word "comprises" and its variants (such as
"comprising", etc.) should not be interpreted as excluding, i.e., they do
not exclude the possibility that what has been described includes other
elements, steps etc.

[0070]In addition, the invention is not limited to the specific
embodiments that have been described but rather also encompasses, for
example, the variants that can be made by a person skilled in the art
(for example, with regard to the choice of materials, dimensions,
components, configuration, etc.), within that inferred from the claims.